Insulating layer for rigid printed circuit boards

ABSTRACT

One or more embodiments contained herein disclose rigid printed circuit boards (PCBs) and methods for manufacturing the same comprising strain resistant layers configured to, among others, minimize defects from occurring in cap layers of the PCBs.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present patent application claims the priority benefit of U.S.Provisional Application No. 61/012,392, which was filed on Dec. 7, 2007.This patent application also claims the priority benefit of U.S.Provisional Application No. 61/016,292, filed on Dec. 21, 2007, and U.S.Provisional Application No. 61/078,315, filed on Jul. 3, 2008, thedisclosures of both of which are hereby expressly incorporated byreference in their entirety.

BACKGROUND

1. Field

The disclosure herein relates to printed circuit boards, and moreparticularly, insulating layers for use with rigid printed circuitboards.

2. Description of the Related Art

Printed circuit boards (PCB) comprise one or more layers of electricallyconductive material such as copper and one or more electricallyinsulating layers such as dielectrics. Multilayer PCBs typicallycomprise two or more inner and/or surface conductive layers formed overand separated by a plurality of insulating layers with holes, vias, andthrough holes providing electrical connection between the various innerconductive layers and other inner conductive layers and/or the surfaceconductive layers.

Several aspects of the PCB manufacturing and assembly processes subjectPCB components to strain or stress (e.g., mechanical, thermal, physical,chemical, and the like). For example, manufacturing exposes PCBs to arange of temperatures, including high soldering temperatures which haveincreased even more in response to the industry's recent adoption oflead-free processes. Strain can cause defects in components, resultingin electrical and/or mechanical failure. For example, thermal strainarising from increasing temperatures can cause cracks in the PCBcomponents, including pad cratering, a type of crack typically occurringin insulating layers that engage surface conductive layers. Variousembodiments disclosed herein contemplate certain more stable anddamage-resistant PCB components for use with rigid PCBs that maysubstantially increase the yield of rigid PCBs while possibly reducingdefects such as voids and cracks and increasing the structural integrityof the rigid PCBs and portions of rigid PCBs such as junctions betweeninsulating layers and surface conductive layers.

SUMMARY

In an embodiment, a device for mounting electrical components comprises:a printed circuit board comprising: a surface conductive layerconfigured to interface with the electrical components; a strainresistant cap layer configured to engage the surface conductive layer,wherein the strain resistant cap layer comprises polyimide; and one ormore rigid insulating layers, wherein at least one of the one or morerigid insulating layers extends throughout the entire length of theprinted circuit board such that the entire printed circuit board definesa rigid printed circuit board.

In accordance with some embodiments, a method of manufacturing printedcircuit boards comprises: providing a component comprising a firstsurface of a strain resistant cap layer engaging a first surface of aconductive layer, wherein the strain resistant cap layer comprisespolyimide; and attaching the component a stack of laminates by attachinga second surface of the strain resistant cap layer to a top surface of afirst layer of the stack of laminates, wherein the stack of laminatescomprises at least one rigid insulating layer extending throughout theentire length of the printed circuit board to define the printed circuitboard comprising entirely rigid portions.

In certain embodiments, a component for manufacturing rigid printedcircuit boards comprises a conductive layer comprising a first surfaceand a second surface; a discardable layer comprising a first surface,wherein the first surface of the discardable layer is attached to thefirst surface of the conductive layer; and a strain resistant layercomprising a first surface, wherein the first surface of the strainresistant layer is attached to the second surface of the conductivelayer, and wherein the strain resistant layer comprises at least twocharacteristics selected from a group of: ductility of at least about15%, Tg of at least about 220° C., and tensile strength of at leastabout 10,000 psi.

In some embodiments, a printed circuit board comprises: a surfaceconductive layer configured to interface with the electrical components,wherein the surface conductive layer comprises rolled-annealed copper; astrain resistant cap layer configured to engage the surface conductivelayer, wherein the strain resistant cap layer comprises polyimide; andone or more rigid insulating layers, wherein at least one of the one ormore rigid insulating layers extends throughout the entire length of theprinted circuit board such that the printed circuit board defines arigid printed circuit board.

In some embodiments, a rigid circuit board comprises a surfaceconductive layer engaging a strain resistant cap layer. In anembodiment, a component for manufacturing printed circuit boards such asrigid printed circuit boards comprises a surface copper layer and astrain resistant layer, wherein the strain resistant layer comprisespolyimide. In a certain embodiment, a rigid PCB comprises one or morestrain resistant layers. Further still, the printed circuit board in oneembodiment comprises: a surface conductive layer configured to interfacewith the electrical components, wherein the surface conductive layercomprises rolled-annealed copper; a strain resistant cap layerconfigured to engage the surface conductive layer, wherein the strainresistant cap layer comprises ductility of at least 15% and tensilestrength of at least 10,000 psi; and one or more rigid insulatinglayers, wherein at least one of the one or more rigid insulating layersextends throughout the entire length of the printed circuit board suchthat the printed circuit board defines a rigid printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will now be described with reference to thedrawings summarized below. These drawings and the associated descriptionare provided to illustrate one or more embodiments described in thepresent patent application and not to limit the scope of the disclosedembodiments.

FIG. 1 depicts an embodiment of a multilayer printed circuit board.

FIG. 2 illustrates another embodiment of a multilayer printed circuitboard comprising via holes and conductive plates.

FIG. 3A illustrates a printed circuit board comprising ball grid array(BGA) packaging.

FIG. 3B is a cross sectional view of an electrical component mounted ona printed circuit board to form a printed circuit board assembly.

FIG. 3C illustrates an embodiment of a printed circuit board showing acap layer engaging a surface conductive layer.

FIG. 3D illustrates an embodiment of a printed circuit board showing acap layer comprising a defect engaging a surface conductive layer.

FIG. 3E illustrates an embodiment of a printed circuit board showing acap layer comprising another defect engaging a surface conductive layer.

FIG. 4 illustrates an embodiment of a printed circuit board comprisingstrain resistant layers.

FIG. 5 illustrates an embodiment of a printed circuit board comprisingstrain resistant layers.

FIG. 6 illustrates an embodiment of a method of manufacturing multilayerprinted circuit board stacks using components comprising discardablematerial.

FIG. 7A illustrates an embodiment of a component for manufacturingprinted circuit boards comprising a discardable layer and strainresistant layers.

FIG. 7B illustrates another embodiment of a component for manufacturingprinted circuit boards comprising a discardable layer and a strainresistant layer.

FIG. 8 is a table listing material characteristics for example strainresistant materials and other insulating materials.

FIG. 9 is a table comparing expansion characteristics of example strainresistant materials and other dielectric materials.

FIG. 10A illustrates an embodiment of a rigid printed circuit board.

FIG. 10B illustrates an embodiment of a rigid printed circuit boardcomprising a strain resistant cap layer.

DETAILED DESCRIPTION

In describing various embodiments in the present application, referencewill be made herein to FIGS. 1-10B of the drawings, in which likenumerals refer to like features unless indicated otherwise.

A. General Description of Non-Limiting Embodiments

The terms “printed circuit boards,” “PCBs,” and “electrical interconnectsystems,” as used in the present patent application, are interchangeableand are broadly defined and comprise, without limitation, any and allsystems that provide, among others, mechanical support to electricalcomponents, electrical connection to and between these electricalcomponents, combinations thereof, and the like. PCBs comprise systemsthat generally include a base platform to support the electricalcomponents (for example, a thin board of insulating material) andconductors such as conductive pathways, surfaces, solderableattachments, and the like to provide an electrical interconnectionbetween the electrical components. PCBs can employ a broad range oftechnologies to support the electrical components (for example,through-hole, surface-mount, mixed-technology, components mounted on oneor both sides, etc.) and can comprise a wide range of single ormultilayer constructions (for example, single-sided, double-sided,multilayer, flexible, rigid-flex, stripline, etc). The variousembodiments herein can apply to PCBs existing at any stage of the PCBmanufacturing process, including, by way of non-limiting examples,partially incomplete PCBs lacking one or more PCB components typicallypresent in more complete PCBs such as, for example, insulating layers,conductive circuit patterns, conductive plates, via holes, and the like.As used throughout this application, the term “rigid PCB” includes itsstandard meaning in the industry and also defines PCBs having nobendable portions. As defined herein, “partially rigid PCBs” broadlyrefers to interconnect systems comprising at least some rigid andnon-bendable portions. Layers belonging to the rigid and non-bendableportions of rigid or partially rigid PCBs can be at least substantiallycoplanar and may lie in the same plane (e.g., horizontal plane, verticalplanes, planes therebetween, etc.) and can be configured to maintain acoplanar structure in operation. PCBs and rigid PCBs can comprise one ormore rigid insulating layers. “PCB assembly” broadly refers to printedcircuit board systems on which electrical components are partially,substantially, or fully mounted (e.g., electrically attached orconnected).

The terms “insulating layer,” “dielectric layer,” and “dielectricsubstrate” are broadly interpreted herein, are interchangeable, includetheir standard meaning in the industry, and describe nonconductive PCBlayers generally configured to resist or substantially resist the flowof electricity and to provide physical support for, among others,conductive layers and electrical components. The term “rigid” as used inconnection with PCB insulating layers (e.g., rigid insulating layers,rigid dielectrics, etc.) is broadly defined and describes insulatinglayers comprising ordinary “rigid materials” including, withoutlimitation, materials that are typically non-bendable and reinforcedwith fiberglass, papers, cotton fabric, asbestos sheet, glass in variousforms such as cloth and continuous filament mat, ceramic material,molybdenum, various types of plastics, etc. Several other rigidmaterials or mixes of rigid materials can be used to produce rigidinsulating layers, including prepregs (short for preimpregnated) suchas, for example, flame retardant (FR) 2 (cellulose paper impregnatedwith phenolic resin), FR-3 (cotton paper impregnated with epoxy), FR-4(epoxy-resin impregnated woven glass cloth), FR-5 (woven glassimpregnated with epoxy), etc. Rigid layers comprise rigid materialsgenerally used to manufacture rigid PCBs or rigid portions of partiallyrigid PCBs.

As used herein, “strain resistant layers” is defined broadly and refersto insulating layers for manufacturing printed circuit boards, includingrigid and partially rigid PCBs, comprising, among others, one or morecharacteristics that can endure more strain (e.g., mechanical, thermal,physical, chemical, and the like) and/or can be more stable (e.g.,thermally, chemically, physically, etc) than ordinary insulating layers,including rigid insulating layers as described herein. Strain resistantlayers comprise a broadly defined array of “strain resistant materials,”including, without limitation, thermosetting and/or thermoplasticplastics, such as, for example, polyimide, polyester, fluorinatedhydrocarbon, polymers, polyacrylate, liquid crystal polymer, syntheticfibers, aramids, fluorocarbons, etc. Strain resistant layers can alsocomprise a mixture of one or more of the thermosetting and/orthermoplastic plastic materials or a mixture of one or more of theplastic materials with other materials (e.g., fillers, hardeners, etc.).

“Cap layer,” as used herein, is broadly defined and describes dielectricsubstrates and insulating layers that interface with or engage theoutermost conductive layers, also referred to herein as “surfaceconductive layers,” such as, for example, surface copper pads. “Surfaceconductive layer,” “outer conductive layer,” or “surface layer” used inconnection with PCB conductive layers broadly refer to the outermostconductive layers of PCBs, such as, for example, surface copper layersand etched surface conductive pads generally configured to engageelectrical devices mounted on the PCBs, such as, for example, electricalcomponents. “Electronic” or “electrical” components broadly describe anyPCB-mountable device capable of handling electricity for which PCBs aredesigned to provide, among others, physical support and/or electricalconnection and without limitation include electrical devices, electronicdevices, electronic circuits, electrical elements, integrated circuits,hybrid systems, and the like.

The term “layer” as used in this application implies a position in thecross section (profile) of PCBs or components of PCBs. A layer in a PCBmay be continuous or discontinuous, and may or may not be planar orsubstantially planar. For example, a PCB may comprise an inner or outerconductive discontinuous layer such as an etched printed circuit layer.As used in relation to one PCB layer in connection with another PCBlayer, the terms “engage” or “attach” or “over” (e.g., as in one layerover another layer) are broadly defined to describe a layer or portionsof the layer directly or indirectly connected or attached to anotherlayer or portions of the other layer. Non-limiting examples of anindirect connection include, for example, a layer in a PCB connected orattached to another layer through an intermediate layer, such as, forexample, a mask, a coating layer, a thin film, soldering material, andthe like. Similarly, “forming,” “depositing,” “positioning,” or“providing,” as used herein in connection with creating or positioningone layer over or on another layer, generally disclose arranging orcreating PCB layers such that at least portions of one layer aredirectly or indirectly engaging at least portions of the other layer. Arigid layer “extending” throughout the entire length of the PCB definesa layer generally provided over the length of the PCB (e.g., may or maynot be continuous, may or may not have same boundaries with the PCB,etc.) such that the PCB is a rigid PCB.

As used herein, the terms “pre-form” or “pre-forming” PCB layercomponents or layers to be used with PCBs define a discontinuity betweenmanufacturing the components and manufacturing PCBs using the pre-formedcomponents such that the component manufacturing and the PCBmanufacturing qualify as “independent manufacturing processes.” Anon-limiting example of independent manufacturing processes includesmanufacturing PCBs using a component manufactured by an entity differentfrom the entity manufacturing the PCBs, such as, without limitation,3^(rd) parties (e.g., original equipment manufacturers, distributors,wholesalers, discount sellers, suppliers, retailers, etc.), affiliates,subsidiaries, parent entities, licensors/licensees, other legallydifferent entities, combinations thereof, and the like. PCB“manufacturing” is broadly defined herein and includes all stages of thePCB manufacturing and assembly process, including, for example,preparing or obtaining materials to make PCB layers, providing at leasta first PCB layer, processing one or more PCB layers to form circuitpatterns separated by insulating layers, assembling a PCB by mounting anelectrical component onto a partially, substantially or fully completedPCB, testing a PCB assembly package comprising electric devices mountedthereon, etc. Various embodiments herein describing manufacturing rigidPCBs are also applicable to manufacturing rigid portions of partiallyrigid PCBs.

Referring now to FIG. 1, an embodiment of a multilayer printed circuitboard (PCB) 100 is illustrated. The PCB 100 comprises first and secondconductive outer or surface layers 120, 120 a, first and secondinsulating layers 125, 125 a, first, second, and third conductive innerlayers 130, 130 a, 130 b, and first and second insulating inner layers135, 135 a. The first and second insulating layers 125, 125 a of FIG. 1engage the first and second surface conductive layers 120, 120 a and,therefore, are cap layers. The conductive inner layers 130, 130 a, 130 bcan be etched to form first, second, and third circuit patterns 123, 123a, 123 b.

As illustrated in FIG. 1, the first surface conductive layer 120 is overthe first insulating layer 125 and the first insulating layer 125 isprovided over the top surface of the first circuit pattern 123. Thefirst circuit pattern 123 a is over the top surface of the firstinsulating inner layer 135, the latter of which is positioned over thesecond circuit pattern 123 b, which in turn is over the top surface ofthe second insulating inner layer 135 a. As shown in FIG. 1, the thirdcircuit pattern 123 b is over the top surface of the second insulatinglayer 125 a and the second insulating layer 125 a is provided over thesecond surface conductive layer 120 a.

The surface conductive layers 120, 120 a and/or the circuit patterns123, 123 a, 123 b can comprise any suitable conductive metals, such as,for example, copper, gold, aluminum, nickel, kovar, steel, resistancealloys, etc. PCB conductive layers are typically made of thin copperfoil. As shown in FIG. 1, at least one of the insulating layers 125, 125a and/or the insulating inner layers 135, 135 a comprises an ordinaryinsulating layer comprising a wide array of rigid materials such asepoxy resin, FR-3, FR-4, etc. In certain embodiments, at least one ofthe insulating layers 125, 125 a and/or the insulating inner layers 135,135 a comprising rigid material is substantially coplanar with at leastone of the surface conductive layers 120, 120 a such that the PCB 100 isa rigid PCB. In certain embodiments, the at least one of the insulatinglayers 125, 125 a and/or the insulating inner layers 135, 135 acomprising rigid material is substantially coextensive (e.g., crosssectional length) with at least one of the surface conductive layers120, 120 a. In various embodiments, the PCB 100 comprises at least onerigid insulating layer (e.g., the first and second insulating layers125, 125 a, the first and second insulating inner layers 135, 135 a, oranother insulating layer not shown) extending through the entire lengthof the PCB 100 such that the PCB 100 is a rigid PCB. Dielectricmaterials, including the insulating layers 125, 125 a and the insulatinginner layers 135, 135 a can be selected based on properties such as, forexample, thermal stability, dielectric constant, flexibility, tensilestrength, and dimensional stability.

FIG. 2 illustrates another embodiment of a multilayer PCB 200 disclosingthe PCB 100 of FIG. 1 further comprising first, second, third, andfourth levels of via holes 250, 250 a, 250 b, 250 c and conductiveplates 265, 265 a, 265 b, 265 c. The via holes 250, 250 a, 250 b, 250 cand the conductive plates 265, 265 a, 265 b, 265 c, the latter being atleast partially over some portions of the via holes 250, 250 a, 250 b,250 c, the surface conductive layers 120, 120 a, and the circuitpatterns 123, 123 a, 123 b, generally are configured to electricallyconnect various conductive layers of the PCB 200, as will be discussedbelow.

As illustrated in FIG. 2, the first level via holes 250 are shownpenetrating the first surface conductive layer 120 and the firstinsulating layer 125. In FIG. 2, the first layer via holes 250 and someportions of the first surface conductive layer 120 are coated with theconductive plate 265. The first level via holes 250 and the conductiveplate 265 connect some portions of the surface conductive layer 120 withsome portions of the first conductive inner layer 130. The second layerof via holes 250 a are shown penetrating the first conductive innerlayer 130 and the first insulating inner layer 135. The second layer viaholes 250 a and some portions of the first conductive inner layer 130are coated with the conductive plate 265 a. The second layer via holes250 a and the conductive plate 265 a connect some portions of the firstconductive inner layer 130 with some portions of the second conductiveinner layer 130 a.

Still with reference to FIG. 2, the third layer of via holes 250 b areshown penetrating the second conductive inner layer 130 a and the secondinsulating inner layer 135 b. The third layer via holes 250 b and someportions of the second conductive inner layer 130 a are coated with theconductive plate 265 b and connect some portions of the secondconductive inner layer 130 a with some portions of the third conductiveinner layer 130 b. The fourth layer via holes 250 c penetrate the thirdconductive inner layer 130 b and the second insulating layer 125 a. Thefourth layer via holes 250 c and portions of the third conductive innerlayer 130 b are coated with the conductive plate 265 c and connect someportions of the third conductive inner layer 130 b with some portions ofthe second surface conductive layer 120 a. In some embodiments, thefirst surface conductive layer 120, the second surface conductive layer120 a, or both the first and second surface conductive layers 120, 120 aare etched to create pads 299, for example, to electrically connect anelectrical component such as a semiconductor chip (not shown) with thePCB 200.

As shown in FIGS. 1 and 2, the PCB 100 and the PCB 200 are provided asnon-limiting illustrative embodiments and although the figures show PCBscomprising four insulating layers (the first and second insulatinglayers 125, 125 a and the first and second insulating inner layers 135,135 a) and five conductive layers (the first and second surfaceconductive layers 120, 120 a and the first, second, and third circuitpatterns 123, 123 a, 123 b) arranged in the configurations disclosedtherein, the various embodiments and features disclosed throughout thisapplication can be used in connection with PCBs comprising a differentnumber (for example, more or fewer than five conductive layers and/orfour insulating layers) and a different arrangement of conductive and/orinsulating layers. For example, although the via holes 250, 250 a, 250b, 250 c of PCB 200 penetrate only a single layer of electricallyconductive layer and a single layer of insulating layer, the via holes250, 250 a, 250 b, 250 c in other embodiments can be configured tocomprise varying lengths penetrating more or fewer layers. In oneembodiment, a solder resist layer can be further deposited on the topsurface of one or both of the outer most conductive layers 120, 120 a.In some embodiments, as least some of the via holes 250, 250 a, 250 b,250 c can be at least partially filled with solder resist material. Incertain embodiments, the PCB 200 can comprise one or more through-holespenetrating one or more of the layers of the PCB 200 to accommodateinsertion of electrical component leads. In some embodiments, at leastone of the first and second insulating layers 125, 125 a or the firstand second insulating inner layers 135, 135 a comprises rigid material.In certain embodiments, portions of the at least one of the first andsecond insulating layers 125, 125 a or the first and second insulatinginner layers 135, 135 a comprising rigid material are coplanar with someportions of the at least one of the surface conductive layers 120, 120 asuch that the PCB 200 comprises at least some rigid portions comprisingthe rigid portions of a partially rigid PCB. In certain embodiments,substantial portions of the at least one of the first and secondinsulating layers 125, 125 a or the first and second insulating innerlayers 135, 135 a comprising rigid material are coplanar with the atleast one of the surface conductive layers 120, 120 a such that the PCB400 is a rigid PCB. In various embodiments, the PCB 400 comprises atleast one rigid insulating layer (e.g., the first and second insulatinglayers 125, 125 a, the first and second insulating inner layers 135, 135a, or another insulating layer not shown) extending through the entirelength of the PCB 400 such that the PCB 400 is a rigid PCB. In someembodiments, the PCB 400 comprises a plurality of rigid insulatinglayers, some of which extend substantially less than the entire lengthof the PCB 400 (e.g., half, a third, etc.), arranged in a manner suchthat the combination of the plurality of rigid insulating layers makesthe PCB 400 a rigid PCB (e.g., a rigid insulating layer extendingroughly through half the length of the PCB 400, another rigid layerextending roughly through the remaining half, etc.).

FIGS. 3A-3E include depictions of various embodiments illustrating anexample defect that can be caused by, among others, the strain (e.g.,thermal strain) put on PCBs during the manufacturing process. FIG. 3A isa top plan view of the top surface 325 of a PCB 300 comprising, forexample, one or more of the PCBs 200 of FIG. 2. The top surface 325 hasthereon a simplified dog bone design comprising conductive pads 320,plated via holes 340, and connectors 330. The PCB 300 comprises a ballgrid array (BGA) mounting technology wherein the array of conductivepads 320 are configured to connect to corresponding conductive pads ofsurface mountable electrical components (not shown) to electricallyattach or mount the electrical components with the PCB 300. In someembodiments, the PCB 300 can be configured to comprise differentelectrical component packaging technologies such as, without limitation,Dual In-line Packaging (DIP), Pin Grid Array (PGA), Leadless ChipCarrier (LCC), Flip-chip BGA (FCBGA), Plastic Quad Flat Pack (PQFP),Small-Outline Integrated Circuit (SOIC), Plastic Leaded Chip Carrier(PLCC), System in Package (SIS), combinations thereof, and the like.

FIG. 3B shows a cross-section view of portions of an electricalcomponent 308, soldering material 307, and a portion of the PCB 300 ofFIG. 3A. A conductive chip pad 305 is attached to the electricalcomponent 308. For simplicity, the PCB 300 of FIG. 3B shows only one ofthe conductive pads 320 attached to the PCB 300 of FIG. 3A. As shown inFIG. 3B, the conductive chip pad 305 of the electrical component 308 canbe electrically connected to the conductive pad 320 of the PCB 300 usingthe soldering material 307. The assembly can be heated, for exampleusing a reflow oven or an infrared heater, to melt the solder ball 307and to thereby mechanically couple the electrical component 308 with thePCB 300. Once coupled, the electrical component 308 and the PCB 300 areelectrically connected, and electric signals from the conductive pad 320can flow to the electrical component 308 through the soldering material307 and the electrically conductive chip pad 305.

During the manufacturing of PCBs, an electrical component assemblyprocess, or normal operation of PCBs, cracks can occur on one or morelayers of the PCBs. One cause of such cracks is the considerable thermalstress (e.g., including mechanical stress arising from changes intemperature) to which PCBs are subjected, for example, during themanufacturing process including heating of the soldering material.Various materials used in the assembly processes, such as insulatinglayers, conductive layers, soldering metals, and electrical componentscan have different coefficients of thermal expansion (CTE), potentiallycausing these materials to expand and contract at different rates inresponse to changes in temperature. As such, thermal stress during thePCB assembly process can arise from mismatches in CTE, both between theelectrical components, including soldering material, and the PCB boardsonto which the electrical components are mounted, and between thedifferent materials which make up the PCB. In the case of a type ofcrack called pad cratering, thermal mismatch or Coefficient of ThermalExpansion (CTE) mismatch, for example between cap layers and surfaceconductive layers, can cause a defect such as a crack in the cap layersas the cap layers and the surface conductive layers respond (e.g.,expand or contract) to temperature changes at unequal rates. Forexample, when heat is applied to soldering material 307, CTE mismatchbetween the conductive pad 320 and portions of the cap layer underneaththe conductive pad 320 can cause portions of the cap layers to moverelative to the conductive pad 320 (e.g., opposite direction),separating some portions of the cap layer from the conductive pad 320.Pad cratering can cause portions of the PCB to be separated or fall off,resulting in mechanical failure in the PCB, or can create a defect inthe flow of electricity in the PCB, causing an electrical failure. Incertain embodiments, thermal stress can cause the conductive pads 320 topartially, substantially, or fully separate from the underlying caplayer. The at least partially separated conductive pads 320 can removeportions of the cap layer still attached to portions of the at leastpartially separated conductive pads 320, thereby creating holes orcraters the cap layer from which the at least partially separatedconductive pads 320 separate. Strain such as thermal strain can alsocause a defect by applying stress to the junction connecting the caplayer and the conductive pad 320 without forming a crack in the caplayer to potentially cause intermittent or thermally sensitiveelectrical or mechanical failures.

Still with reference to 3B, the recent trend of using lead-free PCBmanufacturing processes including lead-free soldering has exacerbatedpad cratering. The leading lead-free alloys used in the PCB assemblyprocess such as tin, bismuth, copper, various proprietary mixtures ofsome of these alloys, and/or other materials have higher melting pointsthan lead-based soldering material, necessitating the use of highertemperatures to melt the soldering material 307 to couple, for example,the semiconductor electrical component 308 and the PCB 300. As CTEs area function of temperature, the application of higher temperatures to thevarious layers of the PCB 300 and the electrical component 308 can puteven more strain on the PCB 300, the various layers of the PCB 300(e.g., between insulating and conductive layers), the electricalcomponent 308, and the various layers of the electrical component 308 byincreasing differences due to thermal expansion, thereby increasingthermal stress.

Still with reference to 3B, the PCB 300 can also be subjected to moremechanical strain, including during the manufacturing process, as aresult of rising manufacturing temperatures. The use of increasingreflow-soldering temperatures can correspondingly increase the hardnessof insulating layers, including cap layers, making these insulatinglayers more brittle and more susceptible to mechanical stress. Further,the leading non-lead based soldering materials typically have harder andstiffer properties than lead-based soldering materials and, therefore,can generate higher mechanical forces on the conductive pads 320 orinsulating layers of the PCB 300 including the cap layers engaging theconductive pads 320. Alone or in combination, these factors can increasethe frequency of cracks, including pad cratering, that can occur ininsulating cap layers engaging the conductive pads 320. In certainembodiments, strain as described herein applies stress to junctionsconnecting insulating layers and conductive layers, causing defects inthe connection (e.g., sever partially or completely, undermineconnectivity, etc.) creating electrical or mechanical failures.

FIGS. 3C-3E illustrate an embodiment of pad cratering that can occur,for example, in an insulating layer 325 positioned below surfaceconductive layers of PCBs, including, for example, the conductive pad320 of FIG. 3B. Although the pad cratering embodied in FIGS. 3C-3E isshown as occurring in the insulating layer 325 underneath the conductivepad 320 of FIG. 3B, FIGS. 3C-3E illustrate only one embodiment andcracks can occur in different layers, including, without limitation, theinsulating inner layers 135, 135 a of FIG. 2, and in insulating layersengaging different conductive layers, such as, without limitation, theconductive inner layers 130, 130 a, 130 b. FIG. 3C shows the conductivepad 320 and the insulating layer 325 (for example, the first insulatinglayer 125 of FIG. 2) engaging the conductive pad 320 under normalcircumstances. FIG. 3D shows the connection between the conductive pad320 and the insulating layer 325, wherein the insulating layer 325 isbeginning to form a crack 370 (pad cratering) as a result of the strainexerted onto the conductive pad 320. As can be seen in FIG. 3D, thecrater 370 separates at least one end of the insulating layer 325 intotop portion 175 and bottom portion 185. FIG. 3E illustrates a moresubstantial pad cratering 380 wherein the top portion 175 of theinsulating layer 325 is separated from the bottom portion 185, likelycausing failure in the PCB 300 or portions of the PCB 300.

B. Detailed Descriptions of Non-Limiting Embodiments

Methods and systems for use with manufacturing, assembling, and usingPCBs, including rigid and partially rigid PCBs, comprising more stable(e.g., thermally, mechanically, physically, etc.) strain resistantlayers to resist damage that can arise from strain and/or stress (e.g.,mechanical, thermal, physical, and the like) will now be described withreference to the accompanying drawings.

FIG. 4 illustrates a multilayer PCB 400 comprising the PCB 100 of FIG. 1and further comprising first and second strain resistant layers 450, 450a. The first surface conductive layer 120 is over the first strainresistant layer 450, the latter of which is over the first insulatinglayer 125. The top surface of the first strain resistant layer 450engages the first surface conductive layer 120 and the bottom surface ofthe first strain resistant layer 450 engages the first insulating layer125. The second strain resistant layer 450 a is over the second surfaceconductive layer 120 a and the second insulating inner layer 125 a isover the second strain resistant layer 450 a. The second strainresistant layer 450 a is between the second surface conductive layer 120a and the second insulating layer 125 a and the first strain resistantlayer 450 is between the first surface conductive layer 120. The bottomsurface of the second strain resistant layer 450 a engages the secondsurface conductive layer 120 a and the top surface of the second strainresistant layer 450 a engages the second insulating layer 125 a. In someembodiments, a pre-formed laminate component comprising the first strainresistant layer 450 engaging the first surface conductive layer 120 or apre-formed laminate component comprising the second strain resistantlayer 450 a engaging the second surface conductive layer 450 b can beused to manufacture the PCB 400 by attaching the pre-formed laminatecomponent to the remaining layers of the PCB 400 (e.g., the first orsecond insulating layers 125, 125 a).

In some embodiments, the strain resistant layers 450, 450 a comprisesuitable commercially available materials, such as, for example, Kapton®polyimide film, available from E. I. du Pont de Nemours and Company(DuPont). In certain embodiments, the PCB 400 comprises pre-formedlayers of the first strain resistant layer 450 engaging the firstsurface conductive layer 120 and/or the second strain resistant layer450 a engaging the second surface conductive layer 450 b. In someembodiments, the PCB 400 comprises commercially available pre-formedcomponents of conductive and strain resistant layers such as, forexample, R/Flex 1000® available from Rogers Corporation and Pyralux® LF,Pyralux® AC, Pyralux® FR, available from DuPont, and the like.

In FIG. 4, the PCB 400 comprises the strain resistant layers 450, 450 a,the surface conductive layers 120, 120 a, the insulating layers 125, 125a, the conductive inner layers 130, 130 a, 130 b, and the insulatinginner layers 135, 135 a. However, the PCB 400 may comprise more or fewerlayers of materials or structures, for example materials or structuresnot illustrated in FIG. 4. In some embodiments, the strain resistantlayers 450, 450 a are configured to engage the first and second surfaceconductive layers 120, 120 a, respectively, with other layers of the PCB400, such as, for example, the insulating layers 125, 125 a,respectively. The PCB 400 may comprise additional layers not shown inFIG. 4 such as cover coats to protect the PCB 400 against corrosion andcontamination, other materials that for example bond various layers ofthe PCB 400, and the like. In certain embodiments, a solder resist layercan be over the top surface of one or both of the outermost surfaceconductive layers 120, 120 a. In some embodiments, the PCB 400 cancomprise a through-hole penetrating one or more of the layers of the PCB400. In certain embodiments, the PCB 400 comprises one or more via holesplated with conductive material. Other various configurations are alsopossible. In some embodiments, the PCB 400 is a single sided and singlelayer PCB. In some embodiments, the PCB 400 is a double sided and singlelayer PCB In an embodiment, the PCB 400 comprises at least one rigidinsulating layer extending throughout the entire length of the PCB 400such that the PCB 400 comprises entirely rigid portions.

Still with reference to FIG. 4, the surface conductive layers 120, 120 acan be manufactured using one or more suitable processes. In certainembodiments, the surface conductive layers 120, 120 a compriseelectrodeposited copper made by, for example, plating copper from acopper anode to a cathode. In some embodiments, the PCB 400 comprisessurface conductive layers 120, 120 a comprising rolled-annealed copperfoil. Rolled-annealed copper foil may be made, for example, by heatingcopper ingots and rolling and annealing the ingots by passing the ingotsthrough a serious of rollers. Certain non-rigid PCBs can comprisesurface conductive layers made of rolled-annealed copper becauserolled-annealed copper comprises qualities such as ductility (ability tostretch without breaking given as a ratio of length of stretched portionand original length) make rolled-annealed copper suitable for non-rigidpurposes such as, for example, flexibility. In some embodiments,ductility of rolled-annealed copper is about 20-45%, including 25%, 30%,35%, and 40%. Rolled-annealed copper has not been used with rigid PCBsfor several reasons, including higher production costs (e.g., comparedwith electrodeposited copper), lack of availability of variousthicknesses and widths, and the perceived lack of benefit of theflexibility of rolled-annealed copper when used in connection with rigidPCBs comprising non-bending portions. The Applicant has recognized thatcertain qualities exhibited by rolled-annealed copper, such asductility, hardness, resistance, etc. can make rolled-annealed coppersuitable for rigid PCBs (e.g., may minimize defects from forming in therigid PCB during lead-free manufacturing). For example, the PCB 400comprising the surface conductive layer 120 comprising rolled-annealedcopper can absorb some thermal stress as elastic deformation, therebylikely reducing defects such as pad cratering from occurring, forexample, in portions of the cap layer underneath the surface conductivelayer 120. In other embodiments, the ability of the PCB 400 to absorbthermal stress may be increased by using the surface conductive layers120, 120 a comprising rolled-annealed copper in combination with thestrain resistant layers 450, 450 a comprising thermal characteristics(e.g., ductility) as further described herein. The surface conductivelayers 120, 120 a can be manufactured using one or more the aboveprocesses, other processes, and combinations thereof.

With continued reference to FIG. 4, the surface conductive layers 120,120 a and the strain resistant layers 450, 450 a can be manufacturedusing one or more suitable processes or methods. In some embodiments, amethod of manufacturing the PCB 400 comprises attaching the surfaceconductive layer 120 to the strain resistant layer 450 using anintermediate layer such as, for example, a bonding intermediate layer(e.g., adhesive).

In some embodiments, a method of manufacturing the PCB 400 comprisesadhesivelessly attaching the surface conductive layers 120, 120 a to thestrain resistant layers 450, 450 a, respectively. The surface conductivelayers 120, 120 a can be adhesivelessly attached to the strain resistantlayers 450, 450 a, respectively, using one or more suitable methods. Thesurface conductive layers 120, 120 a and the strain resistant layers450, 450 a can be adhesivelessly attached using a “cast to foil” processwherein a solution of strain resistant material, such as, for example,polyimide, is applied to the conductive layers 120, 120 a and heated,resulting the strain resistant layer 450, 450 a over the surfaceconductive layers 120, 120 a, respectively. In one embodiment, the PCB400 comprises polyimide (e.g., the strain resistant layer 450)cast-on-copper (e.g., the surface conductive layer 120). The surfaceconductive layers 120, 120 a and the strain resistant layers 450, 450 acan also be adhesivelessly attached using a “sputtering” process whereinconductive cathode (e.g., copper) is bombarded with ions to causeconductive particles impinge on each of the strain resistant layers 450,450 a such that the surface conductive layers 120, 120 a are over thestrain resistant layers 450, 450 a, respectively. In certainembodiments, a method of manufacturing the PCB 400 comprises plating(e.g., electroless plating) conductive material on each of the strainresistant layers 450, 450 a to form the surface conductive layers 120,120 a adhesivelessly engaging the strain resistant layers 450, 450 a,respectively. In some embodiments, a “vapor deposition” method of makingthe PCB 400 comprises vaporizing conductive material such as copper in avacuum chamber and depositing the metal vapor on strain resistantmaterial, thereby forming the strain resistant layers 450, 450 aadhesivelessly engaging the surface conductive layers 120, 120 a,respectively. Further still, a method of making the PCB 400 can comprisefurther treating the surface conductive layers 120, 120 a engaging thestrain resistant layers 450, 450 a, either adhesivelessly or using anintermediate bonding layer such as an adhesive, with other processessuch as, for example, bonding, stabilizing, etc.

Although FIG. 4 illustrates the strain resistant layers 450, 450 apositioned as cap layers and engaging the surface conductive layers 120,120 a, respectively, the strain resistant layers 450, 450 a can besuitably used with the PCB 400 in other configurations. For example,although FIG. 4 shows the strain resistant layer 450 between the surfaceconductive layer 120 and the insulating layer 125, the strain resistantlayer 450 can be the only dielectric between the surface conductivelayer 120 and the first electrically conductive inner layer 130. In someembodiments, additional strain resist materials comprising, for example,polyester, liquid crystal polymer, polyimide, etc. can also be suitablyused as binding material in the central, normally rigid, glasslayer/prepreg portions of PCBs. In still some embodiments, one or moreof the strain resistant layers may be formed (e.g., deposited) elsewherein the PCB 400. In one embodiment, strain resistant layers can bebetween and/or engage inner conductive layers, for example, theconductive inner layer 130 a, and inner insulating layers, such as, forexample, the insulating inner layer 135 a. In some embodiments, thestrain resistant layers 450, 450 a are configured to respectively engagethe first and second surface conductive layers 120, 120 a with otherlayers of the PCB 400, such as, for example, the conductive inner layers130, 130 a.

With continued reference to FIG. 4, the strain resistant layers 450, 450a in certain embodiments comprise at least substantially fiberglass-freematerial. The strain resistant layers 450, 450 a comprisingfiberglass-free material can help to reduce (e.g., minimize, eliminate)the occurrence of electrical failure arising from cathodic/anodicfilament (CAF) growth. CAF growth can result in an electrical shortingfailure when dendritic metal filaments grow along insulating interfaces(typically layers comprising glass fiber/epoxy resin interface), suchas, for example, the insulating inner layers 135, 135 a and/or theinsulating layers 125, 125 a, creating an electrical path between two ormore layers of the PCB 400 that should remain electrically isolated (forexample, portions of the surface conductive layer 120 and portions ofthe conductive inner layer 130 or portions of the conductive inner layer130 and portions of the conductive inner layer 130 a). Strain resistantlayers in accordance with embodiments disclosed herein can reduce (e.g.,minimize, eliminate) CAF growth because, as previously mentioned, thestrain resistant layers (for example, the strain resistant layers 450,450 a) do not comprise or are substantially free of fiberglass materialthat might otherwise provide the surface along which the dendritic metalfilaments may grow. In certain embodiments, one or more strain resistantlayers can be used instead of one or more rigid insulating layers ofPCBs, including rigid PCBs (e.g., instead of one or more of theinsulating inner layers 135, 135 a and/or the insulating layers 125, 125a).

In accordance to certain embodiments, each of the strain resistantlayers 450, 450 a can have a thickness in the range of about 10-30microns, including about 10-15 microns, 12-15 microns, 15-17 microns,15-20 microns, 15-25 microns, and 20-30 microns. In certain embodiments,each of the strain resistant layers 450, 450 a can have a thickness ofabout 12 microns, including about 15 microns, 17 microns, 18 microns, 20microns, 22 microns, 25 microns, and 28 microns. The strain resistantlayers 450, 450 a can comprise thicknesses in the range of about 5-100microns, including about 10-20 microns, 20-30 microns, 30-40 microns,40-50 microns, 50-60 microns, 60-70 microns, 70-80 microns, 80-90microns, 90-100 microns, 100-120 microns, 110-130 microns, and the like.In certain embodiments, each of the strain resistant layers 450, 450 acan have a thickness of about 35 microns, including about 45 microns, 55microns, 65 microns, 75 microns, 85 microns, 95 microns, 105 microns,and the like. In one embodiment, each of the strain resistant layers450, 450 a have thicknesses of less than 10 microns (e.g., 8 microns),thicknesses of greater than 30 microns (e.g., about 32 microns), orboth. In one embodiment, each of the strain resistant layers 450, 450 ahave thicknesses of less than 5 microns (e.g., 1 micron), thicknesses ofgreater than 130 microns (e.g., about 150 microns), or both. Inaccordance to certain embodiments, each of the surface conductive layers120, 120 a can have a thickness in the range of about 15-25 microns,including about 15-17 microns, 16-18 microns, 17-19 microns, 16-19microns, and 18-20 microns. The surface conductive layers 120, 120 a cancomprise thicknesses in the range of about 5-100 microns, includingabout 10-20 microns, 20-30 microns, 30-40 microns, 40-50 microns, 50-60microns, 60-70 microns, 70-80 microns, 80-90 microns, 90-100 microns,100-120 microns, 110-130 microns, and the like. In certain embodiments,each of the surface conductive layers 120, 120 a can have a thickness ofabout 35 microns, including about 45 microns, 55 microns, 65 microns, 75microns, 85 microns, 95 microns, 105 microns, and the like. Inaccordance to various embodiments, each of the surface conductive layers120, 120 a can have a thickness of about 16 microns, including 17microns, 18 microns, 19 microns, 20 microns, 25 microns, 26 microns,etc. In an embodiment, each of the surface conductive layers 120, 120 acan have thicknesses of less than about 15 microns (e.g., about 14microns), a thicknesses of greater than about 25 microns (e.g., 27microns), or both. In one embodiment, each of the surface conductivelayers 120, 120 a can have thicknesses of less than about 5 microns(e.g., about 1 micron), a thicknesses of greater than about 130 microns(e.g., about 150 microns), or both. In an embodiment, the strainresistant layers 450, 450 a can be about 0.0005 inches thick.

FIG. 5 depicts another embodiment of a multilayer PCB 500 comprising thePCB 200 of FIG. 2 and further comprising first and second strainresistant layers 550, 550 a. In some embodiments, the first and secondstrain resistant layers 550, 550 a each comprise a strain resistantmaterial (e.g., polyimide). The first strain resistant layer 550 isbetween the first surface conductive layer 120 and the first insulatinglayer 125. In some embodiments, the top surface of the first strainresistant layer 550 engages the first surface conductive layer 120 andthe bottom surface of the first strain resistant layer 550 engages otherinsulating layers of the PCB 500, such as the first insulating layer125. The first level via holes 250 are formed on the PCB 500 penetratingthe first surface conductive layer 120, the first strain resistant layer550, and the first insulating layer 125. In some embodiments, the firstand second strain resistant layers 550, 550 a are configured to engagethe first and second surface conductive layers 120, 120 a with otherlayers of the PCB 500, such as, for example, the conductive inner layers130, 130 a.

In some embodiments, the strain resistant material comprises polyimide.In certain embodiments, the surface conductive layer 120 and the firststrain resistant layer 550 are pre-formed by electrodepositingconductive material on the first strain resistant layer 550 and thesecond surface conductive layer 120 a and the second strain resistantlayer 550 a are pre-formed by electrodepositing conductive material onthe second strain resistant layer 550 a. In some embodiments, thepre-formed layers each comprise commercially available copper andpolyimide copper clad laminates such as, for example, Pyralux® AF,available from DuPont.

In some embodiments, the first and second strain resistant layers 550,550 a engage the first and second insulating layers 125,125,respectively, using other mechanisms. In certain embodiments, additionalstrain resistant layers may be positioned elsewhere in the PCB 500. Forexample, a strain resistant layer (not shown) may be used as a non-caplayer to engage with one or more of the conductive inner layers 130, 130a, 130 b. In some embodiments, strain resistant layers may be employedinstead of or in combination with one or more of the insulating innerlayers 135, 135 a and/or the insulating layers 125, 125 a.

In accordance with various embodiments disclosed herein, a number ofprocesses and methods can be used to manufacture rigid PCBs (or rigidportions of partially rigid PCBs) and assemblies comprisingsemiconductor and/or circuit components. In some embodiments, a methodsof manufacturing a rigid printed circuit board assembly comprisesproviding a first component comprising a conductive layer and a strainresistant layer, providing a stack of laminates comprising at least oneinsulating layer, and attaching the first component to the stack oflaminates, thereby at least partially (e.g., fully) forming a printedcircuit board. In one embodiment, the stack of laminates comprises atlast one rigid insulating layer. The conductive layer of the firstcomponent can be a surface conductive layer and/or the strain resistantlayer of the first component can be a cap layer. In certain embodiments,the method of manufacturing PCBs further comprises mounting or attachinga circuit component on the printed circuit board to thereby form a rigidprinted circuit board assembly. In some embodiments, providing the firstcomponent comprises providing pre-formed layers of the surfaceconductive layer 120 and the first strain resistant layer 550 and/or thesurface conductive layer 120 a and the second strain resistant layer 550a. In some embodiments, providing the first component comprisesadhesivelessly attaching the conductive layer to the strain resistantlayer. In certain embodiments, the conductive layer of the firstcomponent comprises rolled-annealed copper and/or the strain resistantlayer of the first component comprises polyimide.

In some configurations, providing a stack of laminates comprisesproviding at least one insulating layer comprising a rigid material. Incertain embodiments, providing a stack of laminates comprises formingone or more internal conductive layers engaging the one or moreinsulating layers. In some embodiments, providing the stack of laminatesfurther comprises etching the one or more internal conductive layers,thereby forming circuit patterns (e.g., the circuit patterns 123, 123 a,123 b). With respect to FIG. 5, the first and second insulating layers125, 125 a, the first, second, and third conductive inner layers 130,130 a, 130 b, and first and second insulating inner layers 135, 135 acan form the stack of laminates. In some arrangements, attaching thefirst component to the stack of laminates comprises connecting thestrain resistant layer of the first component with the stack oflaminates. In an embodiment, a strain resistant layer (e.g., the strainresistant layer 550) comprises a first surface and a second surface,wherein the first surface is substantially opposite from the secondsurface (e.g., the top surface of the strain resistant layer 550engaging the bottom surface of the surface copper layer 120 issubstantially opposite from the bottom surface of the strain resistantlayer 550 engaging the top surface of the inner insulating layer 125).In some arrangements, attaching the first component to the stack oflaminates comprises attaching the bottom surface of the strain resistantlayer to the top surface of the stack (e.g., top surface of a firstinsulating layer of the stack such as the inner insulating layer 125 ofFIG. 5). In some configurations, mounting the circuit component onto therigid printed circuit board to form a rigid printed circuit boardassembly comprises connecting the circuit component to the conductivelayer of the first component using soldering material.

FIG. 6 illustrates an embodiment of methods and components formanufacturing PCBs, including rigid and partially rigid PCBs, someportions of which may be disclosed in U.S. Pat. No. 5,674,596, theentire content of which is expressly incorporated herein by reference. Astack 600 of laminates for use with rigid PCBs comprises threecomponents 610, 610 a, 610 b, each comprising a discardable separatorlayer 630, and two PCB laminated layers 611, 612. For illustrativepurposes only, the PCB laminated layers 611, 612 are illustratedsimilarly to the PCB 100 of FIG. 1 (e.g., each comprising insulatingouter layers 125, 125 a, inner conductive layers 130, 130 a, and innerinsulating layers 135, 135 a) but without the surface conductive layers120, 120 a of FIG. 1. The components 610, 610 a, 610 b each can comprisea discardable layer 630 comprising discardable materials such as metals(e.g., aluminum) between two conductive layers 620, 640. The conductivelayers 620, 640 can comprise material different from the discardablelayer 630 (e.g., comprising copper when the discardable layer 630comprises aluminum). The surfaces of the conductive layers 620, 640facing the discardable layer 630 can be processed to be substantiallyfree of particles or defects, and are protected from exposure to variouscontaminants, such as, for example, airborne particles and resin dust,by the discardable layer 630. Although the stack 600 shows the threecomponents 610, 610 a, 610 b and the two PCB laminated layers 611, 612,the configuration is for illustrative purposes only and the stack 600can comprise more or fewer numbers of components and/or PCB laminatelayers.

In an embodiment of manufacturing one or more PCBs, including rigidPCBs, a method comprises releasing the conductive layers 620, 640 fromthe discardable layer 630 and to form the outer conductive layers ofPCBs as described herein. For example, the method can comprise attachingthe conductive layers 620, 640 of the component 610 a as surfaceconductive layers to the insulating outer layer 125 a of the PCBlaminate layer 611 and the insulating outer layer 125 of the PCBlaminate layer 612, respectively. An embodiment of the method cancomprise at least partially separating one or both of the conductivelayers 620, 640 of the component 610 a from the discardable layer 630 ofthe component 610 a. The conductive layer 640 of the component 610 canattach as a surface conductive layer to the insulating outer layer 125of the PCB laminate layer 611. The conductive layer 640 of the component610 can then at least partially separate from the discardable layer 630of the component 610. In certain such embodiments, the method can alsocomprise attaching the conductive layer 620 of the component 610 as asurface conductive layer to the insulating outer layer of another PCBlaminate layer (not shown above the component 610), and the conductivelayer 620 of the component 610 can then at least partially separate fromthe discardable layer 630 of the component 610. The conductive layer 620of the component 610 b can attach as a surface conductive layer to theinsulating layer 125 a of the PCB laminate layer 612. The conductivelayer 620 can then at least partially separate from the discardablelayer 630 of the component 610 b. In certain such embodiments, themethod can comprise attaching the conductive layer 640 as a surfaceconductive layer to the insulating outer layer of another PCB laminatelayer (not shown below the component 610 b), and then at least partiallyseparating the conductive layer 640 of the component 610 b from thediscardable layer 630 of the component 610 b. After separation from theconductive layers 620, 640 of the components 610, 610 a, 610 b, themethod can comprise discarding the discardable layers 630 of thecomponents 610, 610 a, 610 b (e.g., by selective etching of the materialof the discardable layers 630). In certain embodiments, the conductivelayers of the components comprising discardable layer (e.g., theconductive layer 620 of the component 610 a comprising the discardablelayer 630) are first released from the components by, for example, atleast partially separating the conductive layers from the discardablelayer, and then attached to the conductive layers as surface conductivelayers of PCB laminates (e.g., to the insulating layer 125 a of PCBlaminate 611).

FIG. 7A shows a component 700 for manufacturing PCBs comprising twoconductive layers 720, 720 a and a discardable layer 730 comprisingdiscardable materials, including metals, such as, for example, aluminum.The two conductive layers 720, 720 a (e.g., each comprising copper) areover opposite sides of the discardable layer 730. The component 700further comprises stress resistant layers 750, 750 a over the outersurfaces of the conductive layers 720, 720 a. Returning back to FIG. 6,the component 700 of FIG. 7 can be used instead of one or more of thecomponents 610, 610 a, 610 b, thereby attaching the strain resistantlayers 750, 750 a, as well as the conductive layers 720, 720 a, onto oneor more of the PCB laminate layers 611, 612 and/or other PCB laminatelayers (not shown). For example, when using the component 700 in placeof the component 610 a, the method of manufacturing PCBs can compriseattaching the strain resistant layers 750, 750 a to the insulating outerlayer 125 a of the PCB laminate layer 611 and the insulating outer layer125 of the PCB laminate layer 612, respectively. The conductive layers720, 720 a of the component 700, which still are attached to the strainresistant layers 750, 750 a, respectively, also attach to the PCBlaminate layers 611, 612, respectively, as surface conductive layers. Incertain embodiments, the method can comprise at least partiallyseparating one or both of the conductive layers 720, 720 a of thecomponent 700 from the discardable layer 730 of the component 700. In anembodiment, the discardable layer 730 of the component 700 can bediscarded (e.g., by selective etching of the material of the discardablelayer 730). In a further embodiment, the discardable layer 730 isdiscarded after one or both of the conductive layers 720, 720 a at leastpartially separate from the discardable layer 730. In this manner, theconductive layers 720, 720 a and the strain resistant layers 750, 750 acan be effectively attached to PCB laminates 611, 622, respectively. Insome embodiments, the component 700 comprises pre-formed layers of thefirst conductive layer 720 engaging the strain resistant outer layers750, the second conductive layer 720 a engaging the second stressresistant outer layers 750 a, or both. In other embodiments, thepre-formed layers comprise laminated products, such as, for example,DuPont's Pyralux® FR, Pyralux® LF, etc.

FIG. 7B shows an embodiment of another component 710 for use withmanufacturing PCBs, including rigid PCBs. The component 710 comprises adiscardable separator 730 b, a conductive layer 720 b, and a strainresistant layer 750 b. The conductive layer 720 b is over thediscardable layer 730 b and engages the discardable layer 730 b. Thestrain resistant layer 750 b is over the conductive layer 720 b andengages the conductive layer 720 b. Returning back to FIG. 6, thecomponent 710 can be used to provide the strain resistant layer 750 band the conductive layer 720 b over the outermost PCB laminates 611, 612of the stack 600. For example, if the PCB laminate layer 612 is theoutermost PCB laminate layer on the bottom of the stack 600, usingdouble-sided components such as the component 700 could cause at leastone of the conductive layers 720, 720 a of the component 700 and atleast one of the strain resistant layers 750, 750 a of the component 700to be discarded without attaching to anything. The component 710 of FIG.7B can advantageously be used on outer PCB laminates of the stack 600instead of the component 700, thereby eliminating the unnecessarydiscarding of conductive layers and/or strain resistant layers. Thestrain resistant layer 750 b, as well as the conductive layer 720 b, ofthe component 610 b can attach to the insulating layer 125 a of theouter most PCB laminate layer, (e.g., the PCB layer 612). The conductivelayer 720 b can then at least partially separate from the discardablelayer 730 b of the component 710. The discardable layer 730 b of thecomponent 710, for example after at least partial separation from theconductive layer 720 b of the component 710, can be discarded (e.g., byselective etching of the material of the discardable layer 730).

In certain preferred embodiments of the components disclosed in FIGS. 6,7A, and 7B, the conductive layers 620, 640, 750 a, 750 b comprise copperand/or the discardable layers 630, 730 comprise aluminum. However, theconductive layers 620, 640, 750 a, 750 b and/or the discardable layers630, 730 can comprise any suitable metals, including, withoutlimitation, gold, nickel, copper, aluminum, nickel, kovar, steel, andalloys and combinations thereof, without departing from the embodimentsdisclosed in the present application.

C. Strain Resistant Materials and Material Characteristics

Material characteristics and other properties of the strain resistantlayers disclosed in various embodiments herein will now be discussed.The strain resistant layers comprise, among others, mechanical andthermal characteristics that may resist, for example, damage caused bystress, including, without limitation, thermal and mechanical strain. Incertain embodiments, the strain resistant layers may comprise morestable material (e.g., thermally, physically, mechanically, etc.) thanrigid insulating layers as described herein. In some embodiments, thestrain resistant layers can be more dimensionally stable, for example,under high temperatures, than rigid insulating layers. In someembodiments, the strain resistant layers comprise a material suitablefor manufacturing PCBs comprising non-rigid bendable portions, such as,for example, polyester, polyimide, aromatic polyimide, combinationsthereof, and the like. In some embodiments, the strain resistant layerscan be manufactured from a mixture of the above-mentioned or othermaterials. In some embodiments, the strain resistant layers compriseresin such as polyimide having one or more of the followingcharacteristics: fully cured, substantially halogen free, non-glassreinforced, substantially lead free, and substantially fiberglass free.In some embodiments, the strain resistant layers comprise resin such aspolyimide comprising at least two of the following characteristics:fully cured, substantially halogen free, non-glass reinforced,substantially lead free, and substantially fiberglass free. In someembodiments, the strain resistant layers comprise plastics such aspolyimide including a halogen and/or fiberglass. In certain embodiments,the strain resistant layers are substantially free of at least one ofthe following materials: halogen, fiberglass, and lead. The resistantlayers can be substantially free of lead. In one embodiment, the strainresistant layers are substantially free of halogen. In a certainembodiment, the strain resistant layers are substantially free offiberglass. In some embodiments, the strain resistant layers comprisepartially, substantially, or fully cured or uncured polyimide. Thestrain resistant layers can also comprise material that is at leastpartially reinforced with some fiberglass.

The strain resistant layers in accordance with embodiments disclosedherein may provide one or more advantages, including when used inconnection with rigid PCBs. Strain resistant layers and materials asdescribed herein have not been used with rigid PCBs for several reasons,including higher production costs, lack of availability of variousthicknesses and widths, the perceived lack of benefit of characteristicsof these materials when used in connection with rigid PCBs comprisingnon-bending portions, and the like. The Applicant has recognized thatcertain qualities exhibited by strain resistant materials (e.g., one ormore of ductility, hardness, resistance, and the like) can make thestrain resistant layers suitable for rigid PCBs as further describedherein. For example, strain resistant layers comprising low lossmaterial such as polyimide can dissipate less power along longer lengthsthan non-low loss materials and can allow for higher density circuits.In another example, strain resistant layers in accordance with variousembodiments herein can have higher electrical resistance. Strainresistant layers comprising material having higher electrical resistancecan perform better under high temperatures by retaining insulatingproperties under high temperatures that may degrade insulating qualitiesof other types of insulating layers (for example, epoxies). The strainresistant layers comprising material having higher electricalresistance, therefore, can help reduce (e.g., minimize, eliminate)electrical failures caused by, among others, insulating layers rendereddefective by high temperatures.

FIG. 8 illustrates various characteristics of example insulating layers.In accordance with various embodiments disclosed herein, strainresistant layers comprising resins such as, without limitation,polyimide or polyimide-based materials can be configured to reduce(e.g., minimize, eliminate), among other defects, pad cratering. FIG. 8illustrates typical properties for an example strain resistant layercomprising polyimide as well as typical values for FR-4 and High-TempFR-4 rigid insulating layers. The values in FIG. 8 were obtained usingmethods in accordance with IPC TM-650 (Association ConnectingElectronics Industries Test Method Manual by HIS) and/or ASTMInternational Standards Worldwide (e.g., ASTM D-190, ASTM D-696, etc.).

As illustrated in FIG. 8, the strain resistant layers, for examplecomprising polyimide, can be advantageously more ductile than non-strainresistant layers. The ductility (sometimes also referred to aselongation) of an embodiment of a strain resistant layer, for examplecomprising polyimide, can be in the range of about 15-80%, and also canbe about 20%, 25%, 30%, 40%, 45%, 50%, 60%, 65%, 70%, and 75%. Incertain embodiments, the strain resistant layer comprises ductility inthe range of about 15-20%, 20-30%, 30-40%, 20-60%, 40-80%, 50-80%,15-35%, and the like. Further still, the strain resistant layers cancomprise ductility different from the ranges provided herein, and cancomprise ductility less than about 15% (e.g., about 10%), greater thanabout 80% (e.g., about 90%). In some embodiments, the strain resistantlayers comprise ductility of at least about 15%.

The strain resistant layers can comprise higher ductility propertiesthan other insulating materials (for example, ductility of less than 5%for both FR-4 and High-Temp FR-4 epoxies). As previously mentioned,thermal stress resulting from changes in temperature can cause unequalresponses (e.g., rates of expansion, contraction, etc.) in insulatingand non-insulating layers, including cap layers, of PCBs and othermaterials (e.g., surface conductive layers, soldering materials,electrical component conductive pads, etc.). In some situations, thermalstress can cause the surface conductive layers of PCBs and cap layersunderneath the surface conductive layers to move relative to each other(e.g., in opposite directions, in other directions placing strain on theconnection between the cap layers and the surface copper layers, etc.)such that defects such as pad cratering form in or around, among others,the cap layers. The strain resistant layers in accordance withembodiments disclosed herein are more ductile than other insulatinglayers (e.g., FR-4), and can reduce (e.g., minimize, eliminate) padcratering by, among others, at least absorbing some of the thermalstress as elastic deformation. Embodiments of strain resistant layerscomprising ductile material as disclosed herein can also absorbmechanical stress exerted onto components of PCBs (e.g., cap layers),for example, by other more rigid PCB components such as lead-freesoldering material, further reducing the occurring of defects such aspad cratering in the PCB components including in the cap layers.

Although FIG. 8 illustrates characteristics of certain strain resistantlayers, including strain resistant layers comprising polyimide (apolyimide cap layer), these values are representative of only the oneexample of a strain resistant layer and are not a comprehensiverepresentation of all possible strain resistant layers. The variousdisclosed PCB embodiments can suitably comprise strain resistant layershaving different mixtures of polyimide, strain resistant layerscomprising other strain resistant materials such as, for example, liquidcrystal polymer, train resistant layers comprising mixtures of polyimideand other strain resistant materials, or a combination thereof. In someembodiments, strain resistant layers comprising a different mix ofpolyimide and/or other materials may have elongation and otherproperties that are different from FIG. 8 (for example, a strainresistant layer may have a Tg outside the range of about 220-420° C.,ductility outside the range of about 15-80%, etc.).

In accordance with certain embodiments disclosed herein, strainresistant layers (e.g., comprising polyimide) can have favorableproperties that may reduce (e.g., minimize, eliminate) failures causedby, among others, pad cratering. In particular and as can be seen inFIG. 8, strain resistant layers comprising polyimide can have a GlassTransition Temperature (Tg) range of about 220-420° C., and can alsohave Tg values of about 240° C., 290° C., 340° C., 390° C., 440° C., and490° C. In some embodiments, the strain resistant layer comprises Tgvalues of about 210° C., including Tg values of about 215° C., 230° C.,235° C., 245° C., 250° C., 255° C., 265° C., 270° C., 285° C., 300° C.,305° C., 315° C., 330° C., 350° C., 360° C., 370° C., 375° C., 385° C.,400° C., 405° C., 415° C., 430° C., 445° C., 455° C., 460° C., 470° C.,and the like. In certain embodiments, the strain resistant layercomprising material such as polyimide comprise Tg values in the range ofabout 220-450° C., including about 250-300° C., 300-350° C., 350-400°C., 400-450° C., 450-500° C. and the like. In certain embodiments, thestrain resistant layer can comprise Tg values in the range of about220-230° C., including about 230-240° C., 235-245° C., 245-260° C.,260-280° C., 280-290° C., 290-310° C., 310-320° C., 320-340° C.,340-360° C., 360-370° C., 375-395° C., 400-420° C., 405-415° C.,410-430° C., 430-460° C., 250-350° C., 350-450° C., and the like.Further still, the strain resistant layers can comprise Tg valuesdifferent from the ranges provided herein, and can comprise Tg less than220° C. (e.g., 200° C.), greater than 420° C. (e.g., 500° C.), or both.In some embodiments, the strain resistant layers comprise material suchas polyimide having Tg of at least 220° C. The strain resistantmaterials can comprise higher Tg values than other rigid insulatinglayers (e.g., roughly 170° C. and 180° C. for FR-4 and High-Temp FR-4,respectively.

As illustrated in FIG. 8, the total expansion due to temperature up tosolder reflow temperature is lower for a material having higher Tg range(e.g., polyimide) than for a material having a lower Tg (e.g., FR-4).Materials with higher Tg ranges can be advantageous for use asinsulating layers, including for use as cap layers in rigid PCBs,because such materials can maintain their dimensional stability (e.g.,expand and/or contract less in response to, among others, changes intemperature) over a wider temperature range, potentially reducing thelikelihood that cracks will occur in various PCB layers, including caplayers.

As shown in FIG. 8, certain strain resisting layers comprising polyimidecomprise Coefficients of Thermal Expansion (CTE), including CTE valuesin the lateral (X and Y) directions (CTE X,Y) configured to, amongothers, resist defects such as pad cratering that occur in insulatinglayers, including cap layers. CTE X,Y values for certain such strainresistant layers can be lower than the CTE X,Y values for otherinsulating layers, including rigid insulating layers. Materials havinglower CTE X,Y characteristics (e.g., polyimide) are more stable thanmaterials having higher CTE X,Y characteristics (e.g., FR-4, High-TempFR-4) because materials having lower CTE X,Y values generally are lessresponsive (e.g., expand, contract, etc.) to temperature changes. Forexample, FIG. 8 illustrates that CTE X,Y for polyimide above the Tg isin the range of about 20 parts per million per ° C. in temperature(ppm/° C.) and about 42 ppm/° C., including CTE X,Y of about 20 ppm/°C., 25 ppm/° C., 30 ppm/° C., 35 ppm/° C., 38 ppm/° C., 39 ppm/° C., 40ppm/° C., 41 ppm/° C., and 42 ppm/° C. By comparison, FR-4 has a higherCTE X,Y of 140 ppm/° C. and High-Temp FR-4 had a higher CTE X,Y of 45ppm/° C. Thus, the strain resistant layers comprising polyimide expandsless than other insulating layers such as rigid cap layers even undersimilar temperature conditions, and therefore, the strain resistantlayers can reduce thermal forces that apply stress on various componentsof PCBs, including cap layers.

In certain embodiments, the strain resistant layer comprising materialsuch as polyimide comprise CTE X,Y values in the range of about 15-45ppm/° C., including about 20-25 ppm/° C., 20-30 ppm/° C., 25-30 ppm/°C., 20-25 ppm/° C., 25-35 ppm/° C., and the like. Further still, thestrain resistant layers can comprise CTE X,Y values different from theranges provided herein, and can comprise CTE X,Y less than about 20ppm/° C. (e.g., about 15 ppm/° C.), greater than about 42 ppm/° C.(e.g., about 50 ppm/° C.), or both. In some embodiments, the strainresistant layers comprise material having CTE X,Y of about 45 ppm/° C.or less. The strain resistant materials can also comprise CTE of about25 ppm/° C. or less, including about 23 ppm/° C., 21 ppm/° C., 19 ppm/°C., 18 ppm/° C., 10 ppm/° C., and the like.

In certain embodiments, the example strain resistant layers compriseCTE, XY characteristics that better match CTE, XY characteristics ofother components such as surface copper layers. For example, typical CTEX,Y values for copper and tin-lead solder are around 16 ppm/° C. and 27ppm/° C., respectively. The CTE X,Y range of about 20 to 42 ppm/° C.(e.g., 25 ppm/° C.) of the example strain resistant layers are closer tothe CTE X,Y values of copper and tin-lead than the CTE X,Y values ofrigid insulating layers such as FR-4, and therefore, the strainresistant layers and the other components (e.g., surface copper layer)exhibit similar thermal responses under similar thermal conditions(e.g., expand similarly under high temperature). Two layers of differentPCB materials (e.g., a cap layer and a surface copper layer) comprisingsimilar thermal coefficients generally exhibit similar thermal behaviorsand thus can reduce thermal forces that move one layer relative to theother layer so as to create a defect such as a crack in one layer (e.g.,the cap layer). Strain resistant layers comprising CTE values closer toCTE values of surface copper layers than other rigid insulating layersmay be more dimensionally stable than the other rigid insulating layers.Thermally matching the strain resistant layers and other materials suchas surface copper layers and solder materials can reduce thermal stresson the strain resistant layers (cap layers as shown in FIG. 4) or otherinsulating layers of PCBs, and the reduced thermal stress may alsoreduce (e.g., minimize, eliminate) the occurrence of pad cratering inthe cap layers or other layers. Further, the strain resistant layers cancomprise other material (e.g., inorganic filler) to reduce thedifference of CTE between the strain resistant layers and other layers(e.g., surface conductive layers).

The strain resistant layers in accordance with embodiments disclosesherein advantageously comprise tensile strength characteristics suitedfor reducing (e.g., minimizing, eliminating, etc.) damage occurring in,among others, insulating layers such as cap layers. Tensile strengthindicates the level at which stress causes sufficient change in thematerial (e.g., at least partially break, deform, decompose, etc.) suchthat the change at least interferes with the normal operation of thematerial and/or the PCB in which the material is located, for example,by causing electrical or mechanical failure. Therefore, insulatinglayers comprising strain resistant materials having higher tensilestrengths perform better because the strain resistant layers can operateunder stress levels that otherwise cause defects in materials havinglower tensile strengths.

As illustrated in FIG. 8, the strain resistant materials can comprisepolyimide having tensile strength in the range of about 10,000-50,000psi and can include tensile strengths of about 15,000 psi, 20,000 psi,25,000 psi, 30,000 psi, 35,000 psi, 40,000 psi, 45,000 psi, 50,000 psi,53,000 psi, etc. In certain embodiments, the strain resistant layercomprising material such as polyimide comprise tensile strength in therange of about 10,000-20,000 psi, including about 25,000-35,000 psi,35,000-45,000 psi, 15,000-30,000 psi, 25,000-45,000 psi, and the like.Further still, the strain resistant layers can comprise tensile strengthvalues different from the ranges provided herein, and can comprisetensile strength less than about 10,000 psi (e.g., about 5,000 psi),greater than about 50,000 psi (e.g., about 75,000 psi), or both. In someembodiments, the strain resistant layers comprise material such aspolyimide having tensile strength of at least about 10,000 psi.

In accordance with certain embodiments, the strain resistant layerscomprise strain resistant material having a unique combination of two ormore of the aforementioned characteristics (e.g., tensile strength,ductility, CTE X,Y, etc.). Although strain resistant layers comprising,for example, one of the aforementioned characteristics (e.g., ductility)can help reduce or eliminate various defects, strain resistant layerscomprising two or more of theses qualities are even more suited toreduce (e.g., minimize, eliminate, etc.) various types of damage,including pad cratering, that occur in insulating layers such as caplayers. For example, the strain resistant layers 450,450 a of FIG. 4comprising two or more of these characteristic (e.g., tensile strength,ductility, CTE X,Y, etc.) are more apt to resist damage such as padcratering from occurring than other insulating layers comprising, forexample, fewer than two of these characteristics.

In accordance with such certain embodiments, the strain resistant layerscomprise strain resistant materials having two or more of the followingcharacteristics: ductility in the range of about 15-80%, including about15-20%, 20-30%, 30-40%, 20-60%, 40-80%, 50-80%, and 15-35%; Tg in rangeof about 220-420° C., including about 220-250° C., including about250-300° C., 300-350° C., and 350-400° C.; and tensile strength in therange of about 10,000-50,000 psi, including about 10,000-20,000 psi,25,000-35,000 psi, 35,000-45,000 psi, 15,000-30,000 psi, 25,000-45,000psi, and the like.

In accordance with further certain embodiments, the strain resistantlayers comprise two or more of the following characteristics: ductilityof at least about 15%, including about 20%, 25%, 30%, 40%, 45%, 50%,60%, 65%, 70%, 75%, and 85%; Tg of at least about 220° C., includingabout 240° C., 290° C., 340° C., 390° C., 440° C., and 490° C.; andtensile strength of at least about 10,000 psi, including about 15,000psi, 20,000 psi, 25,000 psi, 30,000 psi, 35,000 psi, 40,000 psi, 45,000psi, 50,000 psi, and 53,000 psi. In other embodiments, the strainresistant layers comprise two or more of the following characteristics:ductility of at least about 15%; Tg of at least about 220° C.; tensilestrength of at least about 10,000 psi; and CTE X,Y of 45 ppm/° C. orless.

FIG. 9 illustrates Z-axis expansion for example strain resistant layerscomprising polyimide relative to similarly sized FR-4 and High-TempFR-4, all of which having 1 inch (25.4 millimeter) by 1 inch X, Ydimensions. PCBs comprising the various types of insulating layers weresubjected to high temperatures during soldering electronic components tothe PCBs, for example, about 215° C. during the leaded solder reflowprocess and 245° C. during the lead-free solder reflow process. Attemperatures ranging from 20° C. to Tg, the example strain resistantlayer, FR-4, and High-Temp FR-4 expanded by about 0.094107 millimeters(mm), about 0.053340 mm, about 0.065024 mm, respectively. Attemperatures ranging from Tg to the leaded solder reflow temperature(215° C.), FR-4 expanded by about 0.160020 mm and High-Temp FR-4expanded by about 0.040005 mm whereas the example resistant layerexpanded by an insignificant amount. For temperatures ranging from Tg tolead-free reflow temperature (245° C.), the example strain resistantlayer expanded by about 0.025400 mm, whereas both the FR-4 and theHigh-Temp FR-4 expanded by higher values of about 0.266700 mm and about0.074232, respectively. Total expansion for the example strain resistantmaterial for leaded solder reflow was about 0.094107 mm, which was lessthan each of the total leaded solder reflow expansions of FR-4 andHigh-Temp FR-4 (about 0.119507 mm and about 0.105029 mm, respectively).Total expansion for the example strain resistant material for lead-freesolder reflow was about 0.119507 mm, which was less than each of thetotal lead free solder reflow expansions of FR-4 and High-Temp FR-4(about 0.320040 mm and about 0.139319 mm, respectively). In oneembodiment, the strain resistant layers comprise aromatic polyimide. Assuch, cap layers and other insulating layers comprising the strainresistant layers (e.g., polyimide) as disclosed herein canadvantageously maintain dimensional stability over a wide temperaturerange.

D. Detailed Descriptions of Further Non-Limiting Embodiments

FIGS. 10A and 10B illustrates a schematic diagram of an embodiment of arigid PCB 1000. In FIG. 10A, the PCB 1000 comprises a rigid dielectric1010, a conductive surface layer 1020, and a solder material 1040. ThePCB 1000 optionally comprises a conductive plate 1030 between theconductive surface layer 1020 and the solder material 1040. The rigiddielectric 1010 comprises a rigid material such as, without limitation,standard FR-4 Epoxy or High-Temp FR-4 Epoxy. The conductive surfacelayer 1020 comprises a conductive material such as copper and can beformed by etching the conductive material. The rigid dielectric 1010engages the surface conductive layer 1020. The conductive plate 1030 isover the conductive surface layer 1020. The solder material 1040 isdeposited over the conductive plate 1030. The solder material 1040connects an electrical component (not shown) with the PCB 1000, therebyforming a rigid printed circuit board assembly. As already mentioned,high temperatures, for example, in excess of 400° C. used in lead-freesoldering processes, are applied to the soldering material 1040 toconnect the electrical component with the PCB 1000. Subjecting the PCB1000 and the rigid dielectric layer 1010 to high temperatures can causedefects to occur in the rigid dielectric 1010, for example, underneaththe conductive surface layer 1020.

FIG. 10B shows the PCB 1000 of FIG. 10A comprising an insulating layer1050 between the conductive surface layer 1020 and the rigid dielectric1010. The top surface of the insulating layer 1050 is configured toengage the conductive surface layer 1020 and the bottom surface of theinsulating layer 1050 is configured to engage the rigid dielectric 1010.As previously mentioned, the insulating layer 1050 comprises materialshaving better characteristics (e.g., thermal, mechanical, physical,etc.) than the rigid dielectric layer 1010, such as, for example, higherTg (greater than or equal to about 220° C.). In some embodiments, theinsulating layer 1050 has ductility of greater than or equal to about15%. In various embodiments, the insulating layer 1050 has tensilestrength greater than or equal to about 10,000 psi. In some embodiments,the insulating layer 1050 comprises polyimide. In certain embodiments,the insulating layer 1050 comprises another strain resistant material(e.g., liquid crystal polymer, polyester, etc.). As mentioned above, theinsulating layer 1050 comprises materials that can perform better underhigh temperatures (e.g., expand less, absorb stress, etc.) and thereforea PCB comprising the insulating layer 1050 engaging the surfaceconductive layer 1010 can reduce (e.g., minimize, eliminate) theoccurrence of defects underneath the conductive surface pad 1020including, for example, pad cratering. In some embodiments, a circuitcomponent (not shown), for example an Integrated Circuit (IC) chipcomponent, can be mounted on the PCB 1000 using the solder material1040, thereby forming a printed circuit board assembly.

Further non-limiting specific embodiments of strain resistant layers asdisclosed herein can be found, for example, at FIGS. 1 and 2 and pages3-6, of the above-specified U.S. Provisional App. No. 61/016,292, thecontent of which is hereby entirely incorporated by reference, and FIGS.1-7 of the above-specified U.S. Provisional App. No. 61/078,315, theentire content of which is hereby entirely incorporated by reference.

The various embodiments described herein can also be combined to providefurther embodiments. Related methods, apparatuses, and systems utilizingstrain resistant layers, including, without limitation, polyimidelayers, in rigid printed circuit boards, are described in theabove-referenced provisional applications to which this applicationclaims priority, the entireties of each of which are hereby expresslyincorporated by reference: U.S. Provisional Patent Application Ser. No.61/016,292, which was filed on Dec. 21, 2007, and U.S. ProvisionalApplication No. 61/078,315, which was filed on Jul. 3, 2008. While theabove-listed applications may have been incorporated by reference forparticular subject matter as described earlier in this application, theApplicant intends the entire disclosures of the above-identifiedapplications to be incorporated by reference into the presentapplication, in that any and all of the disclosures in theseincorporated applications may be combined and incorporated with theembodiments described in the present application.

Although the foregoing description has shown, described, and pointed outthe fundamental novel features of the embodiments disclosed herein, itwill be understood that various omissions, substitutions, and changes inthe form of the detail of the apparatus as illustrated, as well as theuses thereof, may be made by those skilled in the art, without departingfrom the spirit or scope of the disclosed embodiments. Consequently, thescope of the present application should not be limited to the foregoingdiscussion, but should be defined by the appended claims.

1. A device for mounting electrical components, the device comprising: aprinted circuit board having a planar dimension many times greater thanany one electrical component mounted thereon, the printed circuit boardcomprising: a surface conductive layer configured to interface with theelectrical components via at least one lead-free solder component,wherein the surface conductive layer comprises copper; a strainresistant cap layer configured to engage the surface conductive layer,wherein the strain resistant cap layer comprises polyimide and aninorganic filler for increasing the strength of the cap layer, thetensile strength of the cap layer being about 25,000-35,000 psi, whereinthe elongation of the cap layer is about 15-35%; and at least one rigidinsulating layers laminated to the strain resistant layer without abonding layer, wherein the at least one rigid insulating layers extendsthroughout the entire length of the printed circuit board such that theentire printed circuit board defines a rigid printed circuit board;wherein the at least one rigid insulating layer has a tensile strengthwhich is at least 1.3 times greater than the strain resistant cap layer.2. The device of claim 1, wherein the strain resistant cap layercomprises at least two characteristics selected from a group of:ductility of at least about 15%, Tg of at least about 220° C., andtensile strength of at least about 25,000 psi.
 3. The device of claim 1,wherein the strain resistant cap layer comprises at least onecharacteristic selected from the group of: fully cured, substantiallyhalogen free, non-glass reinforced, substantially lead free, andsubstantially fiberglass free.
 4. The device of claim 1, wherein thestrain resistant cap layer comprises a CTE X,Y value of about 40 ppm/°C. or less.
 5. The device of claim 1, wherein the strain resistant caplayer has thickness in the range of about 10-30 microns.
 6. The deviceof claim 1, wherein the strain resistant cap layer comprises tensilestrength in the range of about 26.000-32,000 psi.
 7. The device of claim1, wherein the strain resistant cap layer comprises ductility in therange of about 20-30%.
 8. The device of claim 1, wherein the strainresistant cap layer comprises aromatic polyimide.
 9. The device of claim1, wherein the surface conductive layer comprises electrodepositedcopper.
 10. The device of claim 1, further comprising the strainresistant layer cast-on the surface conductive layer.
 11. The device ofclaim 1, wherein the strain resistant cap layer comprises tensilestrength in the range of about 10,000-15,000 psi.
 12. A printed circuitboard having a planar dimension many times greater than any oneelectrical component mounted thereon comprising: a conductive layerconfigured to interface with electrical components mounted on theprinted circuit board; a strain resistant layer defining a cap layerengaging the conductive layer, wherein the strain resistant layercomprises ductility between about 15% and 50% and tensile strength of atleast about 10,000 psi, the strain resistant layer further comprising afiller; and at least one rigid insulating layer laminated to the strainresistant layer, without a bonding layer, the insulating layer extendingthroughout the entire length of the printed circuit board, wherein theentire printed circuit board comprises substantially rigid portions;wherein the rigid insulating layer has a tensile strength that isgreater than the tensile strength of the strain resistant layer.
 13. Theprinted circuit board of claim 12, wherein the strain resistant layercomprises Tg of at least about 220° C.
 14. The printed circuit board ofclaim 12, wherein the strain resistant layer comprises polyimide. 15.The printed circuit board of claim 12, wherein the conductive layercomprises copper.
 16. The printed circuit board of claim 12, wherein theconductive layer comprises rolled-annealed copper.
 17. The printedcircuit board of claim 12, wherein the conductive layer compriseselectrodeposited copper.
 18. The printed circuit board of claim 12,wherein the strain resistant cap layer comprises at least onecharacteristic selected from the group of: fully cured, substantiallyhalogen free, non-glass reinforced, substantially lead free, andsubstantially fiberglass free.
 19. A device for mounting electricalcomponents, the device comprising: a printed circuit board comprising; asurface conductive layer configured to interface with the electricalcomponents via at least one lead-free solder component, wherein thesurface conductive layer comprises copper; a strain resistant cap layerconfigured to engage the surface conductive layer, wherein the strainresistant cap layer comprises polyimide and an inorganic filler, whereinthe elongation of the cap layer is about 15-50%; and at least one rigidinsulating layer laminated to the strain resistant layer, wherein the atleast one rigid insulating layer extends throughout the entire length ofthe printed circuit board such that the entire printed circuit boarddefines a rigid printed circuit board; wherein the rigid insulatinglayer has a tensile strength that is greater than the tensile strengthof the strain resistant layer.
 20. The device of claim 19, wherein thestrain resistant cap layer comprises ductility in the range of about15-35%.
 21. The device of claim 20, wherein the strain resistant caplayer comprises ductility in the range of about 15-20%.
 22. The deviceof claim 19, wherein the rigid insulating layer is laminated to thestrain resistant layer without a bonding layer.